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Blocking AC current — Parallax Forums

Blocking AC current

FlyingFishFingerFlyingFishFinger Posts: 461
edited 2006-02-25 20:33 in General Discussion
Hi!
Phew, back from a tedious half-semester and a little time to work on my Stamp-stuff. I have a voltage regulator (5V switching). Since I have not had time to do stuff I still have the old problem that I brought up a few months ago here. I get 5V DC out, but I also seem to get ~10V AC. Since I cannot seem to eliminate this weird voltage, I was wondering if there is any simple circuit that will allow me to block this current while still passing the direct current to the Stamp (the DC and AC voltage appear to be on the same line).
Thanks
Rafael

Comments

  • ForrestForrest Posts: 1,341
    edited 2006-02-25 18:26
    You should connect the incoming power to a diode bridge and connect the output from the diode bridge to your 5V voltage regulator circuit (with input and output capacitors). See here for more info en.wikipedia.org/wiki/Diode_bridge
  • Robert KubichekRobert Kubichek Posts: 343
    edited 2006-02-25 18:33
    Forrest said...
    You should connect the incoming power to a diode bridge and connect the output from the diode bridge to your 5V voltage regulator circuit (with input and output capacitors). See here for more info en.wikipedia.org/wiki/Diode_bridge


    I don't think that a bridge/fullwave rectifier will work, you would still see the rectified 10vDC.....

    How about a blocking capacitor on the + side ???

    It sounds like a switcher from an old computer or desktop that used the 10v ac for timing...

    Bob N9LVU scool.gif
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2006-02-25 18:43
    Use the bridge, add appropriate filter caps, then run it through an LM2940-5 regulator -- bingo, clean 5 volts. Have a look at the power supply schematic of any of our dev boards; the only thing they don't have is the bridge.

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    Jon Williams
    Applications Engineer, Parallax
  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2006-02-25 19:14
    Well it's one of Gunether Daubach's custom boards...he says he coudn't find the AC current I was talking about, but I'm scared I'll blow my Stamp if it really is there and I use it...it also already has in/out caps on it.
    Rafael
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-02-25 19:41
    · I remember the original thread/subject.
    · Have you tested this with a load -- 100ohms (that'd be 50mA and should likely meet any minimum load requirement.)
  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2006-02-25 20:18
    Would it be enough to hook up a resistor in series with the voltmeter?
    Or should I connect a light or something?
    Rafael
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-02-25 20:33
    · In series with the voltmeter does nothing -- the load should be in parallel with the output (one end to "+" and the other to GND/"-"), not something funny with a meter or some darned thing.· A lamp would be good, a couple would be better, anything to draw some current from it, something appreciable, like 50mA.· Just the same as if you were testing a battery.
    · ** Switching supplies don't like "no load" conditions. **

    Post Edit -- I have added a drawing, should there·be any uncertainty as to my meaning.

    Post Edited (PJ Allen) : 2/25/2006 10:30:43 PM GMT
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